This invention relates to an apparatus for preventing any invasion of a cutting liquid back in a replaceable head type machine tool, and is more particularly directed to an apparatus for preventing any invasion of a cutting liquid into a spindle housing for inserting and supporting a spindle on a working head in the foregoing machine tool.
A known machine tool of this kind is disclosed in Japanese Unexamined Patent Application Publication Sho No. 53-115992, for instance. A driving unit is provided which is movable to advance and retreat in relation to a workpiece set table. An annular rail around the driving unit comprises a movable rail on a front side and a stationary rail on a rear side. Plural working heads are mounted turnably on the annular rail so that any desired one thereof may be selected to be positioned on the movable rail so that by an advance movement of the driving unit, the selected working head is advanced towards the set table together with the movable rail under the coupled condition thereof with the driving unit. The workpiece set on the set table is applied with a predetermined work by a tool on a forward end of a tool spindle provided on the head.
It has been usual hitherto with this type of apparatus that a sealing member is applied to an inner circumference of a forward end portion of the housing in order to prevent a cutting liquid, chips or the like from invading into the spindle housing on the head through an insertion gap around the spindle on a forward end portion thereof.
This type of apparatus, however, is inconvenient in that, if the amount of sealing provided by sealing member decreases as a result of wearing or deterioration thereof, it often happens that the cutting liquid penetrates into the housing. This is especially so in the situation where the spindle is rotated at a high speed as in the case of use of a FB spindle. The cutting liquid is jetted against the tool under a high pressures, so that the cutting liquid is liable to penetrate into the housing. This creates the problem that a lubricant enclosed in a bearing portion in the housing is dissolved by the invading cutting liquid resulting in a decrease of lubrication. As a result, there is liable to occur such a trouble as a seizure of the bearing or the like.
Additionally, also at the time when the working head is released from its coupling with the driving unit and is ready to wait on the stationary rail for the next work, it often happens that the cutting liquid previously adhered to and remaining at a place near the forward end of the housing is drawn into the housing as a result of lowering in an internal pressure of the housing caused by the cooling thereof.